One dead note can drive a player crazy because the rest of the guitar may seem fine. The note dies, chokes, rattles, or loses sustain while everything around it behaves.
There are several suspects
A high fret can choke one note. A flat or worn fret can kill sustain. A bad string can lie. A loose part can steal energy. A neck can have a resonance that fights a particular pitch. On acoustics, the body itself can emphasize or cancel certain frequencies.
Dead note or choking note?
A note that dies because it hits the next fret is different from a note that fades because the instrument resonates oddly. One is mostly geometry. The other can be more complicated. The repair depends on which kind of dead note it is.
Diagnosis beats folklore
The bench approach is to change one variable at a time: string, fret contact, relief, action, pickup height, hardware, and resonance. A single dead note is not always a simple problem, but it usually leaves clues.